The present invention relates generally to automatic light-intensity controls and, more particularly, to an improved light-intensity control system which compensates for "hot-spots", maintains proper lighting contrast, provides easy calibration/recalibration and eliminates lighting zone "cross-talk".
In the prior art various attempts have been made to automatically control the lighting level in buildings and offices or the like. These systems generally utilize a light-level sensing device to sense the ambient light level operated in conjunction with a control device. The level of artificial lighting in the controlled space is modulated in response to the sensed light level to maintain a constant total illumination level. While these devices have met with some success, they suffer from several drawbacks.
The prior art light sensors normally treat theentire controlled space as a unit and, therefore, are sensitive to areas of the illuminated space which, although small, appear much brighter to the light-level sensor. These are known as "hot-spots". If the sensor observes and responds to these hot-spots, this causes the lamps to dim over the whole conditioned space which results in a lower than desirable light level in much of the space. In addition, with the prior art devices there is generally no way to provide contrast maintenance over the entire conditioned space which is an important aspect of good lighting. Also, with the prior art devices, adjacent lighting zones frequently are coupled together. Thus, when one zone increases its lighting level in response to decreased total illumination sensed, others detect the increase and interpret this increase in their zone as a call for less lighting. This is known as "cross-talk" and is undesirable because it may cause undue dimming in portions of the conditioned space.